Page 198 - Photonics Essentials an introduction with experiments

Optical Fibers and Optical Fiber Amplifiers

192 Advanced Topics

Figure 9.1. A schematic diagram of the experimental demonstration by Newton that
light can be guided in a stream of water.

der of 20 dB per km. In the early 1970s, the team of Maurer, Keck,
and Schultz at Corning used the wizardry of glass chemistry to show
that the losses could be as low as 2 dB/km. This discovery heralded
the beginning of serious work on optical fiber telecommunications.
Corning fiber still dominates the world market, but we shall see that
this involves a lot more than lowering the loss, which today is typical-
ly about 0.2 dB/km, making glass fiber more transparent than air (in
most places).
In the 1950s, the telecommunications world was dominated by engi-
neers who had worked on radio and radar during the Second World
War. The vision was that telecommunications would continue to im-
prove by building higher and higher bandwidth transmitters, eventu-
ally using radio and even microwaves to send messages. These engi-
neers were not wrong. The mobile telephone network that everyone
uses is proof that radio has a place in modern communications. These
engineers did lack vision, however.
In the 1960s, engineers had developed optical fibers with relatively
low losses, but there were no convenient sources of light. The semi-
conductor laser was a curiosity existing in a few laboratories, and it
operated at 77 K. Lasers made from Nd-doped glass could be bought
commercially. These emit light at 1060 nm, and are a good match to a
local minimum of the fiber attenuation. On the other hand, these
lasers had to be pumped with flash lamps and they emitted about 10

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